When fuel is supplied to a vehicle engine, the amount of supplied fuel is determined by an engine control unit (“ECU”), and an injector injects fuel into the engine according to the amount of determined fuel so that the fuel is supplied into the engine.
The injector is typically configured of a solenoid valve, and is included in each cylinder. The injector injects fuel for a predetermined injection time in response to a fuel injection signal received from the ECU, to supply the fuel into the engine by the amount of required fuel.
As disclosed in Patent Document 1, an injector has an inherent driving characteristic according to its type or manufacturer. Specifically, as illustrated in FIG. 3A, the time required to close the injector according to an amount of required fuel to fuel pressure has a specific linear relationship depending on the type or manufacturer of the injector. In addition, as illustrated in FIGS. 3B and 4A, the time required to close the injector and the commanded injection time of the injector corresponding thereto have a specific corresponding relationship for each type or manufacturer of the injector. In general, information on the nominal characteristic of the injector is stored in the memory of the ECU when the vehicle is manufactured, and is used to supply fuel into each cylinder according to the amount of required fuel.
However, as illustrated in FIG. 4B, even when the same injectors are used, injectors may have different driving characteristics due to a manufacturing tolerance, or a tolerance of an output end of each injector operated by the ECU and thus a difference in the profile of operating current. Particularly, when a deviation of an injector driving characteristic related to an injector closing time is not compensated for each cylinder, injector closing times vary for each cylinder. For this reason, different amounts of fuel are supplied for each cylinder in spite of the injection command based on the same injection time. Thus, it is difficult to perform the same flow control between cylinders.
In order to correct a deviation between a commanded injection time and an injector closing time for each cylinder, a nominal commanded injection time according to the nominal characteristic curve of the injector is compensated by measuring the actual closing time of the injector corresponding to an injection command for each cylinder, as illustrated in FIG. 4B.
The closing time of the injector is typically sensed and measured through a point of inflection obtained by the multiple differentiation of voltage derived during intermittence. However, since it is difficult to detect a point of inflection in the section of the small amount of fuel indicated by the dotted line in FIG. 4A, the closing time of the injector may not be sensed. In addition, the sensing characteristics of the injector differ for each injector in the small flow section.
As illustrated in FIG. 4B, even when the commanded injection time corresponding to the time required to close the injector is present in the region in which the closing time is sensible, there is a case in which fuel is injected in a non-sensitive region before compensation. In this case, it is problematic whether or not the injector closing time is sensed during flow control.
In particular, since a high-pressure engine is used as a gasoline direct injection (“GDI”) engine due to severe environment-related regulations such as Euro 6c, it is necessary to control a small flow by enlarging a multiple fuel injection method.
Accordingly, in order to accurately control a flow deviation between injectors in respective cylinders in a small flow section, it is necessary to reduce the flow deviation between the injectors by accurately measuring the closing time of an injector valve and feedback controlling the same in the section.
However, the conventional control method when it fails to sense the closing time of the injector in the small flow section is not known. Therefore, it is determined that compensation control is performed only in the section in which a sensing failure is not present, i.e. in the section in which a time required for injection is relatively long.
In this case, since it is impossible to accurately control the time required for injection in the small flow section, it is difficult to accurately compensate for injector driving characteristics.
[Patent Document 1] Korean Patent Laid-open Publication No. 2015-0114078 (Oct. 12, 2015)